1. Field of the Invention
The present invention relates to a golf club with a golf club head having a single keel point. More specifically, the present invention relates to a golf club having a golf club head with a single keel point and a stable face angle.
2. Description of the Related Art
Appearance is everything. This is especially true when it comes to the appearance of a golf club at address. Perceived face angle affects marketability as some golfers are very sensitive to the look of an “open” or especially “closed” club face at address, and this factor may weigh heavily in a purchase decision. Some golfers will not even try a golf club that has a face angle they consider unappealing, regardless of the performance of the club.
The face angle of a golf club is defined as the angle of the face to the grounded sole line with the shaft hole perpendicular to the line of flight. Maltby, Golf Club Design, Fitting, Alteration, & Repair, The Principles & Procedures, 4th Edition, Ralph Maltby Enterprises, (1995). The perceived face angle is different than the measured face angle as would be measured on a device such as a CMM or De La Cruz gage. The measured face angle is based on the orientation of the face normal vector at a point in the center of the face. The perceived face angle is generally influenced by factors such as head outline shape at address and paint edge along the top of the face.
Alternative solutions to overcome the problem of variability of face angle at address include use of a dual keel point or multi-keel point sole shape, however these sole shapes have undesired affects on styling and on sound from striking the ball. Other inventions that allow for adjustments in the lie angle and face angle are also available. One such example is Callaway Golf, U.S. Pat. No. 7,281,985 for a Golf Club Head. The Callaway patent describes a golf club head which allows for the face angle, lie angle, loft angle, and shaft diameter of the golf club to be customized to a golfer. The customization of the face angle is accomplished by providing a golf club head with an insert for orientation of the golf club face angle following the manufacture of the golf club head.
Another example is Ralph Maltby Enterprises, Inc, U.S. Pat. No. 480,484 for Method of Fitting Golf Club to Golfer, which discloses the use of a soleplate which discloses a spherical roll sole toward the toe of a head and a runner toward the heel of the head. The face angle can be adjusted by grinding the runner to slope toward or away from the ball striking face of the head.
A further example is The Yokohama Rubber Co. Ltd., U.S. Pat. No. 5,333,862, for a Wood Type Golf Club. The Yokohama patent discloses ideal ranges of angles for the face angle, lie angle, and angle of center of gravity, such that having a combination of such angles reduces the slice effect.
A further example is Callaway Golf, U.S. Pat. No. 6,475,100 for a Golf Club Head with Adjustable Face Angle. The Callaway Golf patent discloses a club head with an internal hosel and an insert disposed within that internal hosel. The insert allows for the face angle of the golf club to be oriented after manufacturing of the golf club head.
Yet a further example is Callaway Golf, U.S. Pat. No. 6,964,617 for a golf club head with gasket. This patent discloses a golf club head with a gasket. The gasket controls the face angle of the club head. The width of the gasket varies to provide an open face angle club head, a closed face angle club head, or a neutral face angle club head.
Still another example is Callaway Golf, U.S. Pat. No. 7,377,862 for a method for fitting a golf club. The Callaway patent discloses a golf club head that has different hosel section orientations which allow for different face angles.
Woods, and in particular drivers, have historically been designed such that the sole shape (surface contour) is defined for styling or turf interaction purposes. Further, the center of gravity has been positioned in a location relative to the face in order to preferentially affect trajectory of the golf ball. The relationship between the sole shape and center of gravity of the golf club determines the face angle at address (natural sole) for a sole shape having a single contact point at equilibrium. This relationship has not been fully understood and as a result the face angle at address may often be different than intended in the design model. Some golfers are very sensitive to the look of an “open” or especially “closed” club face at address and this factor may weigh heavily in a purchase decision.
The club head design in CAD may orient the head in CAD space such that the face angle is at the desired value. This orientation is arbitrarily constrained and is not necessarily representative of the orientation when a player addresses the club and allows it to find an equilibrium orientation.
Some wood heads may overcome this limitation by use of a dual keel point or multi-keel point sole shape. Sole shapes of this type often have undesired affects on styling and on sound from striking a ball.
As a driver is rotated thru a range of address lie angles the measured face angle will generally change by an amount related to the loft of the face at initial orientation and the range of lie angles rotated thru. For instance, a driver having a 10 degrees loft and 0 degree face angle (also known as “Square”) at a design lie angle of 56 degrees, will have a measured face angle that changes significantly (see FIG. 11) as address lie angle changes from 56 degrees to 40 degrees. This change in measured face angle is generally not perceived by the golfer as it doesn't result in rotation of the club head about a vertical axis. This behavior is widely considered desirable as it provides a consistent “looking” club at address for a wide range of players who may have different lie angles at address.
However, depending on the relative orientation of the club center of gravity (“CG”) and the sole surface in the vicinity of contact with the ground, the measured and perceived face angles may vary unexpectedly at different address lie angles. This is a problem with many current woods which can result in problems with acceptance in the market place. Some golfers won't even try a club that has a face angle they consider unappealing, regardless of the performance of the club. An example of the face angle behavior of such a club is shown in FIG. 12.
It is apparent that the need exists for a golf club head with a stable face angle. Golfers want a golf club with an appealing face angle while golf equipment manufacturers need to provide as much standardization as possible in order to prevent escalation of manufacturing costs. Therefore, although prior art has presented many inventions for providing customization, the prior art has failed to provide a cost effective method for customization.